The present invention relates to a positive-working photoresist composition or, more particularly, to a positive-working photoresist composition for fine processing of semiconductor devices such as ICs and LSIs having high sensitivity, heat resistance and resistance against dry etching without the problem of scum formation.
In compliance with the explosively expanding demand for computerization and the recent trend in the semiconductor technologies toward more and more increased fineness of the semiconductor devices such as LSIs of which the density of integration has surpassed the level of 64 kilobits and is reaching 256 kilobits in VLSIs, photoresist compositions used in the photolithographic processing of semiconductor devices are also required to have improved properties. Some of the requirements for modern photoresist materials include (1) high sensitivity and high contrast, (2) excellent heat resistance, (3) excellent resistance against etching either in a dry process or in a wet process and (4) absence of scumming in development.
As is known, photoresist compositions are classified into negative-working and positive-working ones depending on the changes in the solubility behavior of the material caused by irradiation with actinic rays and various combinations of the photosensitive ingredient and the base resin have been proposed for the respective types of the photoresist compositions. As to the formulation of the positive-working photoresist compositions, in which the resinous ingredient is imparted with increased solubility by exposure to actinic rays, a class of ester compounds of 2,3,4,-trihydroxybenzophenone with naphthoquinone-1,2-diazido-5-sulfonic acid (referred to as esters hereinbelow) have been proposed as a promising photosensitive compound or photosensitizer including: a (4-) monoester compound (referred to as monoester hereinbelow) of the structural formula (I) below (see U.S. Pat. No. 3,106,465) ##STR1## a (3,4-)diester compound (referred to as diester hereinbelow) of the structural formula (II) below (see U.S. Pat. No. 3,148,983 and Japanese Patent Publication No. 37-18015) ##STR2## and a (2,3,4-)triester compound (referred to as triester hereinbelow) of the structural formula below (see U.S. Pat. Nos. 3,046,118 and 3,402,044) ##STR3## in which R is a residue of naphthoquinone-1,2-diazido-5-sulfonic acid (referred to as acid residue hereinbelow) expressed by the formula ##STR4## Photoresist compositions comprising the above described di- and triesters and a novolac resin are also disclosed in U.S. Pat. Nos. 3,148,983 and 3,402,044.
It is generally understood hitherto that the positive-working photoresist compositions comprising the esters and the novolac resin can be imparted with a sufficiently high photosensitivity when the novolac resin has a relatively small molecular weight or the amount of the esters is not excessively large.
The use of a novolac resin having a relatively small molecular weight as is mentioned above, however, is disadvantageous in two respects. Namely, the photoresist film formed of the composition has poor heat resistance and cannot withstand the dry etching as is undertaken in the manufacture of VLSIs and scum or residuum of the photoresist film is frequently found in the recessed corners of the patterned photoresist layer formed by development due to the incomplete removal of the photoresist layer. Decrease of the amount of the esters in the photoresist composition, on the other hand, gives nothing to the solution of the latter problem of the scum formation although the former problem of decreased resistance against heat and dry etching can be solved thereby.